A silicone rubber of low specific gravity is characterized by light weight and excellent heat-resistant and weather-proof properties. Therefore this material finds wide use in the manufacture of items where specific properties of this material can be most efficiently utilized, i.e. various seals, packings, gaskets, 0-rings, or similar automobile parts, as well as coatings for rollers used in copying machines, printers, and facsimile machines. A known low-specific-gravity composition of the aforementioned type comprises an expandable silicone rubber composition produced by incorporating thermoplastic hollow particles into a thermosetting liquid silicone rubber composition under heating (see Japanese Application Hei 5-209,080). A problem associated with this composition, however, is that a foam silicone rubber body obtained after curing the aforementioned composition has a large coefficient of thermal expansion and therefore heating leads to significant changes in its dimensions. For the above reasons, the aforementioned known composition is unacceptable as a material for items, such as coating layers on rollers of copying machines, printers, and facsimile machines, and as automobile gaskets, which require that the composition maintain dimensional accuracy during molding and that articles molded from the silicone rubber maintain dimensional stability during heating or cooling.
The authors have conducted a study aimed at finding a solution to the problems inherent in the prior art and arrived at the present invention. It is an object of the present invention to provide a low-specific-gravity liquid silicone rubber composition, which produces low-specific-gravity rubber that demonstrates excellent dimensional stability after heating, during heating, and during cooling.